Damian Budd

B.Sc. Eng. (Hons) Electronic Engineer, Hobbyist and Private Pilot

150W Audio Power Amplifier

Motivation

The purpose behind this design was a rework of the GGAcoustics 250W amplifier into a compact design with a lower power rating.

Specification

150 Watt RMS Dual mono-block power amplifier.

8 Ohm load nominal down to 4 Ohm (150W – 8 Ohm, 300W – 4 Ohm).

Fixed voltage gain of 27 dB.

Balanced output design with balanced inputs.

Better than 100dB signal to distortion at rated power output.

Description

This design follows on from some work I did whilst I was working for GGAcoustics. I had developed a compact version of the 250W amplifier using SMD components. The circuit boards had been manufactured whilst I was working for GGAcoustics and I had assembled two of them, but did not complete the work on the design whilst I was still employed by GGAcoustics. The partners allowed me to retain the boards after I ceased working for them.


I obtained two 625VA transformers for use with the 150W modules and two 47 000uF low ESR capacitors. I assembled this amplifier on a piece of wood in a similar fashion to my previous modular designs.


Audio performance was as expected since it is essentially an identical design to the 250W amplifier but using surface mount components.


Even after completion of this amplifier I still felt the urge to tinker with it. Although I have a strict method for calculating operating points and component values for most parts of the circuit, there are still a few areas where there is a certain flexibility in the choice of values and operating point. I wanted to experiment further in these areas and see if they had any effect on the sound. I made one simple change that involved a single resistor change and when I sat down to listen to make an assessment of the modification I was absolutely astounded by what I heard. It was as if the amplifier had just been moved up 10dB on the Hi-Fi scale. The amplifier brought forth very subtle sounds and detail. This was especially notable in vocals and it revealed the singers emotions. I was so struck by this improvement in sound that I told one of the partners in GGAcoustics who was in possession of the 250W amplifier, and suggested I could make the same modification to the 250W design. He agreed to this and when I returned the amplifier to him following the modification he also noted the improvement in sound.


Since making this discovery I have yet to investigate it further to develop a better technical understanding of why it has such a profound effect. This is an area I wish to do some further research in. If I can reach a better understanding of what this modification is doing to the audio quality then I can also work out how to optimize the performance of this part of the circuit.


I purchased a pair of VividAudio V1.5 speakers to replace my B&W 603 Series 2's. The B&W's had served me well with many hours of enjoyable and rigorous listening tests, but I got to the point where the B&W's could not match up to the amplifiers performance level and needed to upgrade.

Duration

January 2004 - onwards

 

 The 150W amplifier - it doesn't look pretty, but then they say don't judge a book by its cover (or lack of cover).

 The 150W amplifier driving my Vivid Audio V1.5's and being driven from the SPDIF/DAC.